Field of the Invention
The present invention relates to a radio wave receiver which receives satellite radio waves, a radio-controlled timepiece, a signal obtaining method and a storage medium.
Description of the Related Art
Conventionally, there is a positioning apparatus which receives radio waves from a plurality of positioning satellites of a global navigation system such as a GPS (Global Positioning System) and obtains the present position based on signals (navigation message) included in the radio waves. Such positioning apparatus is able to obtain the accurate present position on the entire globe where satellite radio waves can be received. Therefore, the positioning device is used for various purposes such as navigation and recording of history of the movement of the user, notification of the present position, and distribution of advertisement according to the present position.
Among electronic timepieces (radio-controlled timepieces) which receive a radio wave including date/time information and correct the date/time, some are able to receive the radio wave from the positioning satellite. Among such radio-controlled timepieces, some perform positioning to select local time information, in other words, information regarding time zone or rules for summer time according to the present position. With this, suitable local time can be computed and displayed.
The load of receiving the radio wave from the positioning satellite is very large compared to the load of normal operation of counting and displaying the date and time. This consumes the conventional power source used in the radio-controlled timepiece within a short period of time. Alternatively, if a power source for a high load is used, this leads to the problem of increase in size and weight of the radio-controlled timepiece. Therefore, in timepieces which receive radio waves from the positioning satellite, especially, those which are portable such as a watch, there is a technique to not start reception or to pause reception until directly before the timing that the necessary information is transmitted so that the reception operation time can be shortened.
However, in order to obtain the information necessary from the positioning satellite, the signal included in the radio wave needs to be acquired in advance. The time necessary to acquire the signal depends on the environment when the radio wave is received. Therefore, if the acquiring upper limit time is set too short, the radio wave cannot be acquired and the necessary information cannot be obtained. Alternatively, if the upper limit time is set too long, this leads to increase in power consumption. In view of the above, Japanese Patent Application Laid-Open Publication No. 2012-93281 discloses a technique to change the setting of the acquiring upper limit time according to the frequency of occurrence that the necessary information is transmitted.
However, when a radio wave transmitted from a positioning satellite is received to obtain information necessary for positioning, the amount of time until the necessary information is obtained changes depending on the timing that the acquiring operation ends. In other words, the relation between the acquiring time and the power consumption is not simple, and if the acquiring operation is set uniformly, problems as follows may increase, for example, the power consumption may become large even if the acquiring time is not so long, or the acquiring may be considered to fail even if there is plenty of power left and the information necessary for positioning cannot be obtained.